The present invention relates to a method of piecing yarn in the operation of an open end rotor spinning machine and more particularly to such a method in which an extended length of yarn that is likely to be defective is removed from the yarn package upon detecting a condition indicative of possible defective yarn.
In conventional open end rotor spinning machines the spun yarn is wound on a package and the yarn is continuously monitored as to defects, e.g. a yarn break or yarn thicknesses greater than or less than a predetermined quality range. In the event such a defect is detected, the operation at that spinning station is interrupted until an automatic piecing unit that travels along the spinning stations arrives at that station and performs a piecing operation.
The yarn preceding the interruption is wound onto the winding bobbin or package and the silver feed is stopped with the end of the sliver at the entrance to the spinning station. In preparation for the piecing operation, the rotor and associated elements are cleaned of fiber and yarn remnants either by the piecer or by an automatic cleaning device. The piecing operation then begins with a suction device applied to the package and the package rotated in a reverse direction, with the suction being applied for a sufficient time to assure pick-up of the yarn end, which is drawn off the package and held in the suction device, which guides the yarn for manipulation by the piecer to sever a portion of the end of the yarn, prepare the severed end for piecing, reverse feed of the prepared yarn end into the rotor to pick-up fibers being fed from the sliver, and thereupon restart the spinning operation.
The time of application of suction to the package is of a predetermined length sufficient to normally locate the yarn end on the package and unwind a sufficient length for satisfactory piecing, but limited to an optimal minimum time for normal successful operation without unduly extending the cycle time of the operation so that the piecing cycle time will be as short as possible for efficient overall production by the spinning machine.
Conventionally, a yarn sensor will detect when a piecing operation has been unsuccessful and the operation will then be repeated in an attempt to effect a satisfactory piecing, and if a sequence of unsuccessful attempts has occurred the piecer will provide a malfunction signal at that station to alert the operator, who will manually attempt to correct whatever problem has caused the malfunction.
One of the causes for malfunctioning is when the sliver feed is interrupted for some reason, such as the end of the sliver supply or a break in the sliver reaching the sliver feed. Often, the end of the sliver is of reduced thickness or tapered so that the amount of fiber being combed out of the sliver gradually reduces and results in the yarn becoming thinner over an extended length.
Another cause of malfunctioning occurs when the sliver has a loop or knot formed in it that cannot pass through the sliver feed, causing interruption of the spinning even though sliver is present at the feed.
In the prior art, the normal yarn monitoring is accepted as being sufficient to detect unacceptable yarn size variations in time to interrupt spinning without substantial defective yarn being wound on the package. However, this has been found to be less than satisfactorily reliable under conditions where extended sliver feed variations occur, such as when the sliver is running out or a sliver knot or loop is present.
Conventional piecing operations of the type described for use in open end rotor spinning machines are disclosed in Derichs and Raasch U.S. Pat. No. 4,327,546 and in West German Pat. No. PS 27 25 105.
The present invention provides a method for substantially removing defective yarn that may have been wound on a package immediately prior to the interruption of spinning, and thereby enhancing production and the quality of the resulting yarn.